Field of the Invention
Exemplary embodiments of the present invention relate to a wireless power transfer system and a method of detecting a resonant frequency used in a wireless power transfer, and particularly to a wireless power transfer apparatus having two or more transmission coils which are coupled with one receiver coil, a wireless power transfer method used to the apparatus, and a method of detecting a resonant frequency used in the wireless power transfer.
Description of Related Art
In recent years, technologies relating to plug-in hybrid vehicles and electric vehicles are growing rapidly. Part of or the entire driving force of such a vehicle is electric energy. In addition to a method of connecting to a charger in a wired way and putting a plug into the charger, a wireless charging method is being developed as a method of charging electric energy.
The wireless charging method is divided into an electromagnetic induction method and a resonance type method. In the case of the electromagnetic induction method, the distance capable of power transmission between a transmission coil buried in a parking lot and a receiver coil installed in a vehicle is very short. For this reason, the resonance type method is adopted instead of the electromagnetic induction method in order to secure a longer power transmission length, as disclosed in a related art.
Resonance or an echo refers to a phenomenon in which the amplitude of a vibration system is significantly increased in response to an external force that has the same number of vibrations as the natural frequency of the vibration system and that is periodically received. Resonance refers to a phenomenon generated in all the vibrations, such as a mechanical vibration and an electrical vibration. In general, when an external force capable of a vibration is applied to a vibration system, if the natural frequency of the vibration system is equal to the number of vibrations of the external force, the vibration of the vibration system becomes severe and the amplitude of the vibration system is increased. In the same principle, if a plurality of vibration bodies spaced apart from one another at specific distances is vibrated at the same frequency, the vibration bodies mutually resonate. At this time, resistance between the plurality of vibration bodies is decreased.
A wireless power transmission apparatus using multiple transmission coils has been disclosed as a method for improving charging efficiency and increasing output in the magnetic resonance type method. In the case of transmission unit including a plurality of transmission coils, interference between the plurality of transmission coils must be lowered, and high power transmission efficiency can be obtained when an influence between the plurality of transmission coils is the smallest.
A related art discloses a wireless power transmission apparatus including a plurality of power transmitters for transferring wireless power, wherein a wireless power reception apparatus includes a plurality of power receivers capable of receiving respective wireless power signals having different frequencies. The related art is intended to differently control the resonant frequencies of a plurality of power transmitters and to send power to different reception apparatuses, but is not intended to send power to a single power reception apparatus.